1. Field of the Invention
This invention relates to an illuminating device and a projection apparatus using the same, and is particularly suitable for an apparatus such as a slide projector or a liquid crystal projector adapted to achieve the effective utilization of a beam of light from a light source, illuminate a projected image efficiently and project the projected image onto the surface of a screen by a projection lens.
2. Related Background Art
There have heretofore been proposed various projection apparatuses designed such that the original picture of a projected image displayed on film, a liquid crystal light valve (liquid crystal display element) or the like is magnified and projected onto the surface of a screen.
Of these, there have been proposed various projection apparatuses designed such that in order to enhance the utilization efficiency of light, beams of light from a light source are converted into a polarized beam of light which illuminates the liquid crystal display element.
FIG. 7 of the accompanying drawings is a plan view showing the essential portions of the optical system of a projection apparatus according to the conventional art, and FIG. 8 of the accompanying drawings is a side view showing the essential portions of FIG. 7. These figures shows a case where a transmission type liquid crystal panel (liquid crystal light valve) is used as a projected image 72 and this image is magnified and projected by a projection lens 71.
In FIGS. 7 and 8, the reference numeral 73 designates a white light source comprising, for example, a halogen lamp, a metal halide lamp or the like. The reference numeral 74 denotes a reflector comprising a parabolic or otherwise shaped reflecting surface, which effectively directs a beam of light from the white light source 73 toward a polarizing conversion element 70.
The polarization converting element 70 has the optical function of causing an incident beam of light to emerge as a polarized beam of light (P-polarized light). The polarizing conversion element 70 has a polarizing beam splitter 75 for transmitting P-polarized light therethrough and reflecting S-polarized light, a polarizing rotatable element 77 having a quarter wavelength plate and a reflecting surface for converting the S-polarized light from the polarized beam splitter 75 into P-polarized light and reflecting it, and a reflecting mirror 76.
In FIGS. 7 and 8, a beam of light La including the P-polarized light and S-polarized light from the light source 73 is made into two polarized lights P.sub.1 and P.sub.2 by the polarizing conversion element 70, and these P-polarized lights P.sub.1, and P.sub.2 are directed to a condenser lens 78, and a liquid crystal panel 72 is illuminated by a beam of light condensed by the condenser lens 78.
The reference numeral 71 designates a projection lens which projects an image displayed on the liquid crystal panel 72 onto a screen (not shown).
In the projection apparatus shown in FIGS. 7 and 8, the emergent light from the liquid crystal panel 72 is greatly widened in a plane containing both the normal to the polarizing beam splitter 75 and the normal to the reflecting mirror 76 (the plane of the drawing sheet of FIG. 7, hereinafter referred to as the "polarizing conversion plane").
On the other hand, the expanse of the beam of light in a plane perpendicular to the polarizing conversion plane (the plane of the drawing sheet of FIG. 8) is small as compared with that in the polarizing conversion plane. In the projection apparatus according to the conventional art, a beam of light of which the expanses in the polarizing conversion plane and a plane orthogonal thereto differ from each other has been condensed by the condenser lens 78 comprising a spherical lens and the liquid crystal panel 72 has been illuminated by this beam of light. This has led to the problem that the utilization efficiency of the beam of light is low.